First rule of a fight: Always give more than you get. — Taken from Bite the Dust western movie
Surprisingly that first rule of a fight is also the first rule of marketing: Always give more than you get. No matter what you are marketing, whether books, products, services, coaching, or even trinkets, that first rule still applies.
If you want people to buy what you are selling, offer them something of value first. Always give more than you get.